This invention relates to a device for correcting twist of a transfer belt rounded in a pipe shape of a pipe conveyor.
A pipe conveyor has been known, whose endless transfer belt is rounded over its major part in a pipe shape into which a powdery or granular material is enclosed to be continuously transferred. FIGS. 1 to 4 illustrate such a pipe conveyor by way of example.
In the known pipe conveyor shown in FIGS. 1 to 4, an endless flexible transfer belt 1 has an elastic tendency of rounding about its longitudinal axis into a pipe shape. As shown in FIG. 1, the flexible transfer belt 1 extends around a front driving drum 2 and a rear driven drum 3 and is flattened at drums 2 and 3.
A plurality of support frames 4 each in the form of a rectangular frame are arranged in the advancing direction of the transfer belt 1 with substantially equal intervals and connected with one another by means of connecting rods 5 extending in parallel with the advancing direction of the transfer belt 1. As shown in FIG. 2, each of the support frames 4 is divided into two chambers, an upper chamber 4a in which the advancing run 1a of the transfer belt 1 passes and a lower chamber 4b in which the returning run 1b of the transfer belt 1 passes.
In each of the upper and lower chambers 4a and 4b, a plurality of shape-holding rollers 6 are rotatably supported in a circle and spaced circumferentially substantially equidistant one relative to the other.
The advancing run 1a of the transfer belt 1 in a flattened state is driven around the driven drum 3 from its lower side to the upper side and then guided by the support rollers 7 and 8 supporting the lower surface and side surfaces of the run 1a so that the advancing run 1a is progressively rounded into a trough or eavesgutter shape with the aid of its elastic tendency.
Before the advancing run 1a of the transfer belt 1 has not been rounded sufficiently, a powdery or granular material 10 to be transferred is poured onto the advancing run 1a from a hopper 9 provided above the driven drum 3.
The advancing run 1a of the transfer belt 1 is then advanced into the upper chamber 4a of the nearmost support frame 4 to be guided by the shape-holding rollers 6. As a result, the advancing run 1a of the transfer belt 1 is rounded into a pipe shape and side edges thereof are overlapped with each other on the upper side thereof to enclose the material 10 in the pipe-shaped transfer belt 1.
The pipe-shaped advancing run 1a enclosing therein the material 10 is supported on its circumference by the shape-holding rollers 6 and advances keeping its pipe shape together with the material 10 therein.
After leaving the forwardmost support frame 4 near the forward driving drum 2, the advancing run 1a passes through a belt flattening unit (not shown) during which the advancing run 1a is flattened so that the powdery or granular material 10 is poured into a receiving box 11 provided forwardly below the driving drum 2. The belt flattening unit is constructed similar to and substantially in point symmetry of the material enclosing portion shown in FIG. 3.
After leaving the driving drum 2, the returning run 1b of the transfer belt 1 is rounded into a pipe shape in the same manner as described above and passes through the lower chambers 4b of the support frames 4 to return to the driven drum 3. The transfer belt 1 is circulated around the driving and driven drums 2 and 3 in this manner.
However, in the event that the distance between the driving and driven drums 2 and 3 of the pipe conveyor is long, the pipe-shaped transfer belt 1 is frequently twisted about its longitudinal axis due to (a) wrong positions of the shape-holding rollers, (b) errors in accuracy in manufacturing the shape-holding rollers and support portions therefor and (c) irregular wear of the shape-holding rollers.
In order to overcome this problem, a correction device has been proposed for preventing or correcting the twisting of the pipe-shaped belt of a pipe conveyor. In the proposed correction device, a shape-holding roller 6 is arranged as a correction roller at a location where the transfer belt 1 rounded in the pipe shape tends to twist as shown in FIG. 4. The correction roller 6 is inclined such that one end of the roller located on the side of the transfer belt 1 tending to twist is positioned forward of the other end in the advancing direction of the transfer belt 1. In this manner, the correction roller 6 gives the transfer belt 1 twisting forces in a direction opposite to the direction in which the transfer belt 1 tends to twist, thereby preventing the twisting of the pipe conveyor.
In this correcting device, however, the correcting roller contacts the transfer belt 1 only at one point so that sufficient twisting forces could not be given to the transfer belt. In order to eliminate this disadvantage, plural correcting rollers should be provided to increase the contact points with the transfer belt to increase the twisting forces against the twisting tendency of the transfer belt.
However, the plural correction rollers must be individually inclined relative to the advancing direction of the pipe-shaped belt. This operation is very troublesome and time-consuming and an apparatus for this purpose becomes prohibitively complicated.